Megalomma coloratum ( Chamberlin, 1919 )

Tovar-Hernández, María Ana & Carrera-Parra, Luis F., 2011, Megalomma Johansson, 1925 (Polychaeta: Sabellidae) from America and other world-wide localities, and phylogenetic relationships within the genus 2861, Zootaxa 2861 (1), pp. 1-71 : 25-31

Megalomma coloratum ( Chamberlin, 1919)

Figures 7A–L , 8A , 9A–S , 10A–B , 28B , 29B

Potamilla clara Chamberlin, 1919: 20 .

Potamilla colorata Chamberlin, 1919: 21 .

Megalomma coloratum .— Knight-Jones, 1997: 318, Figs 2M–T .— Tovar-Hernández et al. 2009: 326–327, Figs 2c, g , 3e–f , 4f– g .

Type material examined. [ MCZ] 2173, holotype of Potamilla colorata Chamberlin, 1919 , California, Laguna Beach, low tide, Coll. W. A. Hilton, incomplete (last posterior abdominal segments are missing). [ MCZ] 2171 , holotype of Potamilla clara Chamberlin, 1919 ( Fig. 15C, E, I ), California, Laguna Beach, low tide, Coll. W. A. Hilton, complete but broken in anterior abdomen .

Additional material examined. [ ECOSUR] Baja California Norte, México, Ensenada, Playa las Rosas, July 30, 1987, Coll. SISV (11 specs, one female). Villa las Rosas, March 06, 2004 (2 specs). Bahía de Todos Santos, Coll. SISV (3 specs). Baja California Sur, México, La Paz, CICIMAR, March 01, 2004, Coll. PSS, 50 cm, on basaltic rock (3 specs). Sinaloa, México, Mazatlán, Playa Cerritos, Facultad de Ciencias del Mar, February 27, 2004, on rock oyster covered with red and green algae, 4 m, Coll. Esteban (7 specs, 1 juvenile, one female); February 22, 2004, 12 m (10 specs). Nayarit, México, Islas Marías, November 02, 1979, Coll. SISV (1 spec.). Nayarit, North of Bucerias, March 09, 2008, 20° 45’ 44.7’’ N 105° 21’ 28.6’’W, Coll PSS, in oyster, OH-P 0293 (1 spec). Nayarit, La Cruz de Huanacaxtle, Vallarta Garden, February 23, 2008, 20° 45’ 4.3’’ N, 105° 22’ 25.7’’ W, Coll PSS, in coralline rock, OH-P 0294 (1 spec). Nayarit, La Cruz de Huanacaxtle, Vallarta Garden, February 23, 2008, 20° 45’ 4.3’’ N, 105° 22’ 25.7’’ W, Coll PSS, in coralline rock, OH-P 0295 (1 spec). Nayarit, North of Bucerias, March 09, 2008, 20° 45’ 44.7’’ N, 105° 21’ 28.6’’ W, Coll PSS, in oyster, OH-P 0296 (1 spec). Nayarit, North of Bucerias, March 09, 2008, 20° 45’ 44.7’’ N, 105° 21’ 28.6’’ W, Coll PSS, in oyster, OH-P 0299 (1 spec). [ EMU] Baja California Sur, México, Playa el Tesoro, EMU –4464, Coll. LIB, July 17, 1996 (1 spec.). Sinaloa, México, Mazatlán port, EMU 8914–8953, 2009, on metallic buoys, 50 cm depth, Station 1: 23º 12’ 13’’ N, 106º 24’ 31.4’’ W, Sta. 1–I (1 spec.), Sta. 1– III (1 spec.), Sta. 1–IV (3 specs), Sta. 1– V (2 specs), Sta. 1– VI (5 specs), Sta. 1–VII (8 specs), Sta. 1–VIII (4 specs), Sta. 1–IX (1 spec.), Sta. 1–X (1 spec.). Station 2: 23º 12’ 13’’ N, 106º 24’ 30.1’’ W, Sta. 2–I (1 spec.), Sta. 2–II (2 specs), Sta. 2– III (8 specs), Sta. 2–IV (11 specs), Sta. 2– V (20 specs), Sta. 2–VII (2 specs). Sta. 3: 23º 11’ 48.7’’ N, 106º 24’ 31’’ W, Sta. 3–I (3 specs), Sta. 3–II (3 specs), Sta. 3–IV (7 specs), Sta. 3– V (9 specs), Sta. 3– VI (8 specs), Sta. 3–VII (14 specs), Sta. 3–VIII (3 specs), Sta. 3–IX (1 spec.), Sta. 3–X (2 spec.), Sta. 3–XII (1 spec.). Sta. 4: 23º 11’ 31.1’’ N, 106º 24’ 43.9’’ W, Sta. 4–I (1 spec.), Sta. 4–II (1 spec.), Sta. 4–IV (2 specs), Sta. 4– V (15 specs), Sta. 4– VI (1 spec.), Sta. 4–VII (4 specs). Sta. 5: 23º 11’ 8.9’’ N, 106º 24’ 55.8’’ W, Sta. 5–I (5 specs), Sta. 5–II (9 specs), Sta. 5– III (3 specs), Sta. 5–IV (1 spec.), Sta. 5– V (10 specs), Sta. 5– VI (5 spec.), Sta. 5–VII (12 specs), Sta. 5–VIII (7 specs), Sta. 5–XII (5 specs). Nayarit, México, Punta Raza, EMU –5113, Coll. LIB, April 11, 1996, coralline algae (1 spec.); EMU –5114 (1 spec.). [ LACM – AHF] California, USA, Point Dume, St. 404, POIDUM, SubID 4246, 34.00867º N, 118.79386º W, Coll. Marine Pollution Studies Lab/Moss Landing Marine Laboratories, Invasive Species Survey, July 16, 2007, low rocky intertidal, lots of Chondrachanthus, some Codium , Ulva , tunicates, anemones, small laminarians and coralline mats (8 specs). Point Dume, Sta. 404, MLML – 155, 1 DORG 471, 1 R –C–1, SB ¼, 0471, Coll. Marine Pollution Studies Lab/Moss Landing Marine Laboratories, Invasive Species Survey, January 22, 2005, low rocky intertidal (36 specs). Point Dume, Sta. 404, MLML –155, 1 DORG 249, SR–2, Coll. Marine Pollution Studies Lab/Moss Landing Marine Laboratories, Invasive Species Survey, April 05, 2005, 5.4 m (30 specs). Velero III, 003488, Sta. 1139–40, 33º 50’ 30’’ N, 118º 24’ 15’’ W, off Redondo Beach, 3 m, sand (1 spec.). Sinaloa, México, Mazatlán, F3363, N 15196 , n 10118, reef 3.2 km N of Mazatlán, Colls E. Yale & Dawson, June 7, 1952, among algal clumps (3 specs).

Diagnosis. Eyes in dorsalmost and fifth dorsal radioles (spherical); dorsal margin of collar fused to faecal groove; a glandular ring on segment 3; thoracic chaetae Type C; abdominal chaetae broadly hooded.

Description. Branchial crown length 2.94±0.77 mm (n = 100; 1.1– 5 mm), as long as thorax ( Figs 7A , 8A , 9A ), with 15±2 pairs of radioles (n = 100; 8–21 pairs). Branchial lobes semi-circular ( Fig. 9E ). Radiolar bases olive green. Radioles with several narrow red or purple bands distributed over outer and lateral radiole margins and adjacent pinnules, each band occupies a space of 4–6 pairs of pinnules. Outer surfaces of radioles quadrangular basally, rounded distally. Sub-distal compound eyes spherical, present in dorsalmost pair of radioles (23%, n= 100) or dorsalmost and fifth dorsal radioles (77%, n= 100) ( Figs 7G , 9N ). Eyes from fifth dorsalmost radiolar pair smaller than dorsalmost ones ( Figs 7H , 9O–P ). Dorsalmost pair of radioles rigid, erect and longer than other radioles ( Figs 7E , 9B ); ommatidia purple with minute small, white lens; and epithelium near to tip wider than posterior epithelium ( Fig. 9N ). All radioles with short tips ( Fig. 7F ). Dorsal collar margins square, fused to faecal groove, forming broad gap ( Figs 7C, E , 9B–C ). Dorsal lappets absent. Dorsal pockets present ( Figs 7B–C , 9B–C ). Epithelium of dorsal pockets translucent and very narrow, as a membrane ( Fig. 7E ). Ventral lappets rounded, not overlapped, as long as ventral shield of collar ( Figs 7D , 9H–I ). Anterior peristomial ring not exposed. Lateral collar margins of collar covering base of radioles ( Figs 7B–C , 9A ). Mouth located in middle of anterior peristomial ring. Two small patches of nuchal organs presented near mouth and two horns of basal lateral skeleton ( Fig. 9E ). Dorsal lips red colored, erect, triangular about 1/4 length of branchial crown, with mid-rib ( Fig. 9D ). Dorsal pinnular appendages present. Ventral lips about one quarter the length of dorsal lips, broadly rounded ( Fig. 9D ). Ventral sacs present. Caruncle and keel absent. Body plump, cylindrical, ( Figs 7A , 8A ) green olive or pale with ventral shields cream colored and white spots surrounding the lateral sides of the faecal groove and dispersing in all thoracic dorsal epithelium. A whitish glandular ring on segment 3 ( Fig. 7C ). Total thorax-abdomen length 13.41±5.16 mm (n = 100; 4.1– 28 mm) (25 mm holotype), and maximum width 2.04±0.56 mm (n = 100; 0.8–3.8 mm) (2.2 mm holotype) throughout most of thorax. Thorax with 8±1 segments (n = 100; 4–8 segments). Thoracic tori longest on chaetigers 2–3. Tori in chaetigers 2–3 occupy the entire distance between notopodia and ventral shield margins ( Figs 7B , 8A ), contacting shields ( Figs 7D , 8A ). Notopodial fascicles with superior group of elongate, narrowly hooded chaetae ( Fig. 9J ); an inferior group of chaetae Type C ( Figs 9K , 28B ). Thoracic uncini with main fang surmounted by 8–10 rows of numerous minute teeth ( Fig. 29B ), handles 1.5x length of main fang; not extending beyond base of shaft of companion chaetae ( Fig. 9R–S ). Companion chaetae with teardrop-shaped membranes ( Figs 9R–S , 29B ). Tori slightly shorter than those on chaetiger 7 ( Figs 7I , 8A ). Abdominal segments 42±7 (n = 100; 28–64 segments) (43 holotype). Abdominal chaetae broadly hooded ( Fig. 9L–M ); chaetae in posterior row longer than those in anterior row. Abdominal uncini with main fang surmounted by 8–10 rows of numerous minute teeth ( Fig. 9G ). Pygidium broadly rounded ( Figs 7J , 8A ), sometimes forming two or three lobes ( Fig. 7L ). Three groups of 4–5 red pygidial eyespots, each unequalsized ( Fig. 7J–K ). Tubes covered with fine sand grains, and brown algae incrustrating.

GAMETES: From 100 specimens selected from southern Gulf of California, 91% were sexually mature (32% males, 59% females) and 9% unripe. Gametes in mature females are distributed mostly from first abdominal chaetiger to the posterior abdomen, visible through the epithelium between notopodium and neuropodium. Ovogenesis is continuous throughout the entire year, except for November (no specimens were found) and asynchronous as indicated by change in shape (rounded to polygonal) ( Fig. 9F ), the appearance of the cytoplasm and oocyte size: 103.8±45.27 µm (n = 72; 30–180 µm). In males, sperm is distributed from median to posterior abdomen. Sperm morphology was described in Tovar-Hernández et al. (2009). Based on branchial crown and body colour, M. coloratum does not show sexual dimorphism.

SPECIMEN VARIATION: Among specimens from Southern Gulf of California, the number of radiolar eyes was found to vary. The most common condition is the presence of two pairs of eyes in dorsalmost and fifth dorsalmost radioles (77%, n = 100) while eyes only present in dorsalmost radioles is less common (23%, n = 100). In the phylogenetic analysis presented here, this character (character 3) was scored as state 5, i.e. eyes only in dorsalmost and fifth dorsal radioles, as this was the most common distribution.

GROWTH: The relationship between the body length (y) and the number of abdominal segments (x) is described by the power function y= 0.0086x 1.9528 (r= 0.786, p<0.001, n = 100) indicating a continuous growth in M. coloratum ( Fig. 10A ). Body length (x) was significantly correlated with the branchial crown length (y) and is described by the power function y= 0.6629x 0.5775 (r= 0.837, p<0.001, n = 100) ( Fig. 10B ).

BARCODE: Nucleotide sequences between 433–616 bp of the section of COI gene used for barcoding were obtained from four specimens, two from La Cruz de Huanacaxtle, Nayarit, Mexican Pacific ( ECOSUR OH-P0294 , ECOSUR OH-P0295 ) and two from North of Bucerias , Nayarit, Mexican Pacific ( ECOSUR OH-P0296 , ECOSUR OH-P0299 ). The averange evolutionary divergence over the four sequence pairs was 0.9 %.

Remarks. Chamberlin in 1919 described Potamilla clara and P. colorata from low tide in Laguna Beach, California. Original descriptions of both species are brief, do not include diagnostic characters and lack illustrations. Hartman (1938) stated that the type of P. clara is a Megalomma and has affinities with M. roulei (Gravier) . Later, in the catalogue of the polychaetes of the world, Hartman (1959) listed the type of Potamilla colorata as Megalomma sp. Hartman (1969) recorded M. roulei from Corona del Mar, southern California, but her diagnosis is a translation of original description by Gravier (1908a), illustrations were redrawn from Gravier (1909) and her materials were not located at LACM in order to confirm identification. At the end of her diagnosis (pp. 710) Hartman stated that “The record from California may refer to Megalomma pigmentum , if it is shown that the oculate radioles have short, instead of long free tips”. Later, in 1995, Knight-Jones labeled the type of P. colorata as “this is not synonymous with M. roulei but a good species of Megalomma ”. Knight-Jones (1997) synonymized M. clara with M. modestum ( de Quatrefages, 1866) and provided a redescription for M. coloratum . In this study, the synonymy between M. clara with M. modestum proposed by Knight-Jones is not supported since both species have distinguishable features (see remarks on M. modestum ) and M. roulei is declared as insertae sedis (see remarks on M. roulei ). Based on examination of both types ( M. clara and M. coloratum ), these constitute the same species. Apparently, pigmentation was the only feature used by Chamberlin to describe the taxa as different species. Individuals of M. coloratum from Mazatlán show some variation in body color: some bodies are olive green, others pale, and radioles have narrow red or purple bands distributed over outer and lateral radiole margins.

As stated above, original descriptions of M. clara and M. coloratum both are brief, do not include diagnostic characters and lack illustrations. Both species names were simultaneously published by Chamberlin (1919): M. clara on page 20 and M. coloratum on page 21. We follow the recommendations of article 23.9 (and subsequents) of the International Code of Zoological Nomenclature (1999) to consider M. clara as a nomen oblitum and M. coloratum as a nomen protectum since the last name has been widely used in the literature. Furthermore, the type material of M. coloratum was characterized and illustrated by Knight-Jones (1997) and Tovar-Hernández et al. (2009) provided a complete description of the morphological features including some reproductive characters.

The most distinctive character separating M. coloratum from other species from the tropical Eastern Pacific ( M. carunculata , M. circumspectum , M. gesae , M. pacifici and M. pigmentum ) is the presence of a dorsal, broad whitish glandular ring on segment 3. On the other hand, M. cinctum from Taiwan has two glandular rings on segments 2 and 3 respectively, but in M. cinctum the branchial crown is shorter than the thorax (as long as thorax in M. coloratum ) and the radiolar tips are short dorsally, increasing gradually towards ventral radioles (all short in M. coloratum ).

The specimens reviewed here agree with the description provided by Knight-Jones (1997) for the type of M. coloratum , described from Laguna Beach (California) except that the type has just one pair of subdistal eyes in the dorsalmost radioles. All adult specimens reviewed here, have eyes in dorsalmost and fifth dorsalmost radioles (77%, n = 100) while in juveniles, eyes are only present in dorsalmost radioles (23%, n = 100). This variation is not surprising since as Fitzhugh (2003) pointed out, there exists variation in the number of radiolar eyes in paratypes of M. cinctum , although the most common condition is the presence of only one pair of eyes on the dorsalmost radioles. For M. interrupta, Capa and Murray (2009) recorded the presence of eyes only in dorsalmost and lateral radioles, but the eyes in lateral radioles can be absent entirely from some specimens.

Information on the reproductive biology of species of Megalomma is scarce, but in M. coloratum and in M. vesiculosum , M. bioculatum and M. carunculata gonochorism and gametes distributed in abdominal segments seems to be a pattern. Megalomma coloratum is native in the Californian Province, known from Mazatlán and southern California ( USA) from intertidal and shallow waters (12 m). In the Mazatlán port ( México) it is a very common hull fouling species, found on floating docks, metal buoys, and also on rock oysters covered with red and green algae. On metal buoys it reaches densities about 4–80 ind/m 2.

Figures

FIGURE 2. Megalomma acrophthalmos (Grube, 1878). A) Thorax, dorsal view; B) thorax, ventral view; C) collar and anterior segments, ventral view; D) peristomium, frontal view; E) thoracic chaetigers; F) dorsal and ventral lips; G) collar and anterior segments, dorsal view; H–I) inferior thoracic chaetae type B; J) dorsalmost radiolar eye; K) eye from a lateral radiole; L) eye from a ventral radiole. A–L) Specimens from Philippines, USNM, 38683. Abbreviations: apr anterior peristomial ring; ca caruncle; d dorsum; dl dorsal lip; dlc dorsal lappets of collar; nl notopodial lobe; v ventrum; vl ventral lobe; vs ventral sacs; vsc ventral shield of collar. Scale bars: A–D, G) 1 mm; E) 0.5 mm; F) 1 mm; H–I) 50 µm; J–L) 0.3 mm.

FIGURE 3. Megalomma bioculatum (Ehlers, 1887). A) Thorax, dorsal view; B) same, ventral view; C) dorsalmost radiolar eye. A–C) Specimen from Florida, MCZ, 47066. Abbreviation: apr anterior peristomial ring. Scale bars: A–B) 1 mm; C) 0.3 mm.

FIGURE 4. Megalomma circumspectum (Moore, 1923). A) Thorax, dorsal view; B) same, ventral view; C) same, lateral view; D) ventral sacs as indicated with arrows, branchial crown removed; E) posterior end; F) eyes from dorsal radioles; G) dorsalmost radiolar eye; H) eye from 2nd dorsal radiole; I) eye from a lateral radiole; J) ventralmost ocular spot. A–J) Specimens from La Paz, México, ECOSUR. Scale bars: A–C, E) 1 mm; D) 0.5 mm; F) 2 mm; G–J) 0.3 mm.

FIGURE 7. Megalomma coloratum (Chamberlin, 1919). A) Body, lateral view; B) thorax, lateral view; C) glandular ridge on chaetiger 3 as indicated with arrow; D) thorax, ventral view; E) branchial crown and thorax, dorsal view; F) ventralmost radiole; G) dorsalmost radiolar eye; H) eye from 5th dorsal radiole; I) abdominal tori; J–L) pygidiums. A–L) Specimens from Mazatlán, México, ECOSUR. Scale bars: A, E) 10 mm; B–D) 3 mm; F–H) 0.3 mm; I–L) 3 mm.

FIGURE 8. Scanning electronic micrographs of body and caruncle. A) Lateral view of Megalomma coloratum (Chamberlin, 1919) from Mazatlán, México, ECOSUR; B–C) lateral and dorsal views of caruncle of Megalomma lobiferum (Ehlers, 1887) from Ria Lagartos, México, ECOSUR. Scale bars: A) 1 mm, B–C) 0.2 mm.

FIGURE 9. Megalomma coloratum (Chamberlin, 1919). A) Body, lateral view; B) branchial crown, dorsal view; C) thorax, dorsal view; D) dorsal and ventral lips; E) peristomium, frontal view; F) oocytes; G) abdominal uncinus; H–I) thorax, ventral views; J) superior thoracic narrowly hooded chaeta; K) inferior thoracic chaeta type C; L–M) abdominal broadly hooded chaetae; N) dorsalmost radiolar eyes; O–P) eyes from from 5th dorsal radiole in adult and juvenile stages, respectively; Q) ventral radiole; R–S) thoracic uncini and companion chaetae. A–S) Specimens from Mazatlán, México, ECOSUR. Abbreviations: bls basal lateral skeleton; d dorsum; dl dorsal lip; ep epithelium; no nuchal organ; rs radiolar skeleton; v ventrum; vl ventral lip. Scale bars: A–E, H–I) 1 mm; F) 15 µm; G, J–M, R–S) 20 µm; N) 125 µm.

FIGURE 10. Relationships between biometrical features in Megalomma coloratum (Chamberlin, 1919).

FIGURE 15. Megalomma lanigera (Grube, 1846). A, D) Thorax, dorsal view; B) collar, dorsal view; C) collar, ventral view; E) thorax, ventral view; F) ventral and dorsal lip; G) dorsalmost radiolar eye, spherical; H) spiraled eye from a dorsal radiole; I) oval eye from a lateral radiole; J) spherical eye from a ventral radiole. A–C, G–J) Specimens from the Aegean Sea, USNM, 97444; D–F) specimen from Naples, MCZ, 1517. Abbreviations: dl dorsal lip; vl ventral lip. Scale bars: A–F) 2 mm; G–J) 0.25 mm.

FIGURE 28. Scanning electronic micrographs of thoracic and abdominal chaetae. A–F) Thoracic chaetae; G–H) abdominal chaetae. A–C, E) Type C (paleate); D) type B; G) broadly hooded; H) narrowly hooded. A, G) Megalomma circumspectum from La Paz, México, ECOSUR, B) Megalomma coloratum from Mazatlán, México, ECOSUR; C) Megalomma heterops from Campeche, Mexico, ECOSUR; D) Megalomma lobiferum from Colón, Panama, ECOSUR; E) Megalomma pigmentum from Bahía San Quintín, México, ECOSUR; F, H) Megalomma splendidum from Pt. Vicente Light, California, LACM, 2357–53. Scale bars: A–F) 100 µm; G–H) 50 µm.

FIGURE 29. Scanning electronic micrographs of uncini and companion chaetae. A–G) Thoracic uncini and companion chaetae. A) Megalomma circumspectum from La Paz, México, ECOSUR, B) Megalomma coloratum from Mazatlán, México, ECO- SUR; C) Megalomma heterops from Campeche, Mexico, ECOSUR; D) Megalomma lobiferum from Colón, Panama, ECOSUR; E) Megalomma pigmentum from Bahía San Quintín, México, ECOSUR; F) Megalomma splendidum from Pt. Vicente Light, California, LACM, 2357–53. G) Parasabella pallida from Mazatlán, EMU. Scale bars: A–D) 100 µm; E–G) 20 µm.